


Saiki K and Assassination Classroom Crossover

by Ultraviollett



Category: Assassination Classroom, 斉木楠雄のΨ難 | Saiki Kusuo no Sai-nan | The Disastrous Life of Saiki K.
Genre: Alternate Reality, Assassination, Crossover, Gen
Language: English
Status: Completed
Published: 2019-03-17
Updated: 2019-03-17
Packaged: 2019-11-22 22:35:57
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,294
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18142907
Author URL: https://archiveofourown.org/users/Ultraviollett/pseuds/Ultraviollett
Summary: Saiki tries to hide his psychic powers from the assassination classroom when he finds himself in their world. Oneshot.





	Saiki K and Assassination Classroom Crossover

**Author's Note:**

> this was written for an ask on my tumblr @suckerforsaikik

Saiki needed to stop getting himself into these situations. He didn’t know which gods felt the need to torment him like they did, but an angry letter of complaint to their office wasn’t enough to make up for what happened.   
It started as soon as he woke up. Approximately 0.0076 seconds after he got out of his bed, Saiki had noticed something wasn’t right.His limiter had fallen out during his sleep, and was now partially under the pillow. His bed and the better chunk of his room were submerged in sand, which went on for miles. Using his clairvoyance, Saiki still couldn’t see any people for a good 50 kilometres. He had found himself in the middle of the desert.  
“Yare yare, I must’ve teleported.”  
He then had tried teleporting to his house, but he couldn’t find it. He went through the whole neighbourhood, but his dad and mom didn’t seem to… exist? He even checked the whole country, But popping up all over Japan attracted the attention of a few parties.   
And that eventually ended up with him here, With a government agent prattling on about whatever threat the world faced. After revealing his telekinesis on a surveillance camera (thankfully they never found out about his teleportation), the government of Japan had noticed him, and had immediately dragged him to a secret government bunker, talking about how they knew he had special powers. Not that he was listening. Instead, he was worrying over what had happened to everyone he know. The latest theory he had come up with was he had hopped a dimension. It only happened once before, and ended with him running from powerful espers from the 7th division of Claw. He soon realized it would take a day to get back to his normal dimension when he was trying to get back, so that was probably the minimum amount of time he’d have to spend here.  
“What a cliche trope” Saiki sighed. “I’ll just have to play along, I guess”  
“-the reward is 30 billion yen to kill that yellow monster. Will you do it?” The annoying side character agent, who introduced himself as Shiro, finished.   
Saiki rolled his eyes. Even if he’d rather spend the day taking advantage of this universe’s coffee jelly, he knew he couldn’t escape the plot. If he tried running, he would just get dragged back into it for some stupid reason, or he’d be pulled into another, more ridiculous, story. It was the only thing that could beat him.  
A nod confirmed his alliance.  
“Excellent! I’ll get you prepared.” Saiki’s mind-reading abilities told him Shiro wasn’t the most mentally stable, but he figured he’d have a few episodes before Shiro went full crazy.  
“Time to get you enrolled in the assassination classroom.”  
\---  
(Somewhere in a sketchy government facility)  
A bloodstained report smacked onto the desk of the prime minister.   
“We have intel.” the spy who had delivered the file spoke, with his toque shading his eyes, and you could only see his dark pupils drilling down into your head.  
“What’s it aboot?” The prime minister's eyes had seen his fair share of wars, they were dark and unbreakable like a beaver’s den. He pulled the files toward him, examining the files with the intensity of as if they were tickets to a professional hockey game.  
“The Japanese have been keeping secrets from us, sir. They have been hosting a dangerous octopus creature, who says they’ll destroy the Earth next March.”  
“Those bastards.” The prime minister stood up from his desk, causing his chair to scrape the floor as it moved away from him.  
“When I’m done with them, I’ll show them no mercy.” He furrowed his brows. “I’d bet a toonie they thought we couldn’t help because we’re a ‘peaceful’ country. I’ll show them… when we BLOW UP THAT MONSTER OURSELVES!!”  
“How do you plan to accomplish that, sir?”  
“Heat seeking missiles. We aim it right at the students so that damn octopus can’t escape, then we bomb the whole thing with anti-teacher pellets.”  
“Sorry for doubting your plan, sir.”  
“Sorry for making you doubt my plan.”  
“Sorry.”  
“Sorry.”  
\---  
“I hear we’re getting another student transfer, Kayano!” Nagisa stopped to chat with his fellow student on the way to their mountain school.  
“Do you think they’ll be normal this time?” Kayana said.  
“Doubtful” Itona appeared. “The only transfer students we have are freaks. I had tentacles, Ritsu’s an assassination machine, and Karma has too many problems to be ‘normal’.” he listed the transfer students’ ‘quirks’ on his fingers.  
“You might want to stop insulting me,” behind Itona, Karma stood. He smirked, then said “But I wouldn’t disagree.”  
Everyone made their way to class, where KoroSensei was waiting.  
“Hello class.” He tittered. “ The new transfer student comes today, and he has ALREADY challenged me to a fight, so we’re moving quite fast. Ooh, telekinesis? How intriguing!”  
After staring at the note intently, KoroSensei held it up, showing japanese kanas spelling out the time and place for meeting, along with the students known powers.  
“Now please be patient, everyone. The student should arrive right--”  
The door to the classroom blew open. Shiro stepped into the scene, with Saiki a few seconds behind him, yet already regretting it.  
“Hi.” Saiki said.   
Stepping into the classroom, The minds of the students told Saiki about the previous fights of different rivals of Korosensei. All of them had failed, obviously. They tried to kill him, got beaten badly, then learned the value of friendship and working together. It seemed that was what was expected of him as a transfer. Saiki could at least help speed the process up.  
'Alright,’ he thought, ‘ I guess I have to do it.’  
He held up his hands in surrender.  
“Oh no. You are too strong, I can see it now. There is no way I can beat you. I'm so sorry, Shiro, I guess I'm giving up.” He walked off to the empty seat in the corner of the classroom, right next to a window. He smirked. A few more hours and he'd be out of this classroom .  
“W-What?!” Shiro sputtered, stepping closer to Saiki with an intent to murder, “You’re supposed to fight. Get up and KILL HIM!!” he reached to grab Saiki’s shoulder’s before Korosensei’s tentacles pulled him away.  
“You’re not allowed to hurt any of my students, Shiro.” Korosensei said, smiling. “Please excuse yourself from this classroom.”  
Shiro left, albeit slowly. Saiki’s recently created plan was going well.  
As Korosensei started the lesson, a student with flashy red hair (‘Karma Akabane’ Saiki noticed) leaned over to talk to him from the other desk.  
“So, I heard you had telekinesis.” Karma face was two inches from Saiki. Saiki couldn’t really deny his powers here. He nodded.  
“Interesting!” His face was now just an inch away. “Can I have an example?”  
Yare yare. Saiki waved his hands, and a spoon flew into his hand from a nearby lunchbox. Letting go of it so it could float on its own, the metal spoon bent before Karma’s widening eyes. He let out a gasp, making everyone turn to see the spoon that was levitating thanks to a certain psychic’s powers. Now he had an audience.  
“Wow! I guess it’s true. How much power do you have? Can you lift a car? A train? Could you fix the moon?”  
“Why would I need to-” Shoot. That was close to revealing himself as an outsider. His telepathy showed him the broken crescent moon that all the class was thinking about. Could he fix it? He would have to take out his limiter and turn it back seven years, though it wouldn’t be hard theoretically. But if he said yes, that would mean they would ask him to fix it. It also wouldn’t make sense to how he could fix a whole moon and not defeat a yellow octopus man. Lying was the better option here. “I mean, no, Nothing bigger than spoons.”   
“Um, okay.” The whole class was staring at him now. He could tell they were suspicious. He just had to switch the subject, and then they would forget.  
“So what are those weird pink balls on your head?”  
Shoot. He had forgotten to telepathically suggest they were hairpins. Being the center of attention was too dangerous.  
“They’re my hairpins.” Everyone seemed to accept that, thank the gods.  
“Wow! Can I pull them out and see them?” one classmate reached for his head.  
“No.”  
Yare yare. He might not survive today.  
\---  
As Saiki was being tortured by the students of 3-E, Korosensei was sitting read The Great Gatsby. Even when he was thoroughly enjoying his book, his nose caught the faint smell of chemicals. Normally this wouldn’t be the biggest issue, but the chemicals were a fuel-oxidizer mixture, they were up in the air, and they were coming closer at a rate too fast to be a plane. Missiles, then. He could smell out the steam of infrared electricity, so they were heat-seeking missiles, specifically. Why would anyone send heat-seeking missiles to him? He didn’t produce that much heat, so the missile would more likely go to actual people like-  
The children.   
They were aiming for the schoolchildren, to keep him here. Korosensei couldn’t smell it now, but he bet there was also an anti-sensei missile searing through the sky towards him.  
How could he solve this? He needed to stop the missiles, firstly. Should he tell the students? No, that would only worry them about problem with an obvious solution.  
He flew off from his desk in the classroom. At Mach 20, disabling the missiles would be easier than stopping them physically with his lack of strength. Then he would have to bury them in the ocean, or maybe space. Speeding up to the closest missile, he noticed a Canadian flag design on its side.  
“Canada, hmm? It’s always the quiet ones.”  
He tried to open up the hatch to the missiles wires, but his tentacles burst as he touched the metal plating.   
“Anti-sensei plating.” that made it harder. He could go back and grab his napkin to hold it, but he couldn’t navigate the wire system accurately with such a huge handicap. The only option was to evacuate the students and hopefully get out of the missiles range.  
He flew back to the classroom, where a certain psychic was sitting.  
Of course, Saiki knew about the missiles. With a quick check using clairvoyance, he counted 3 in total. Heading straight for them at about Mach 15. There was enough explosives to decimate the whole mountain. Korosensei may try and save all his students, but there were only 20 seconds left. He wouldn’t make it.  
Korosensei quickly shoved his students out the door of the classroom. He talked quickly as he persuaded them out of the building, but he was too agitated to fully explain the situation. Now there were 15 seconds. The missiles could be seen before Saiki and rest of the students were all outdoors. Everyone immediately realized what KoroSensei had been trying to do, and started to sprint, but no one here was fast enough to escape except Korosensei, and he would not abandon his students. 10 seconds. They seemed to realize the couldn’t outrun their death, so they just stood, motionless, wondering what would happen next. Less than 5 seconds left.  
\---  
Saiki knew he had to do it. They would question it, and ask him why he hadn’t used his powers. But even if he hated confrontation, and talking, and socializing, that wouldn’t matter if they were dead. His rule of not interfering would be broken, but he could make an exception. No matter what excuse he made to himself, he knew he wouldn’t run away.  
Two seconds left.  
Saiki calmly stepped forwards to the missiles, putting himself in front of all his classmates. His hands stretched out before him. Like they were frozen in time, all three missiles slowed to a stop, five feet away from the students they were to kill.   
But that was only a temporary solution. Taking out his limiter, Saiki set the missiles to seven years in the past. Plates of metal materialized to take their place, and fell to the grass. The clattered onto the ground unceremoniously  
No one spoke.   
“Wow.” Karma was the first to break the silence, “One question. How?”  
“I’m uh… not from around here.” Saiki fiddled with his hands too much to be normal. He’d rather get hit by a missile than be asked awkward questions in front of a crowd.  
“You’re American??!”  
“No, that’s-” Why was everyone so stupid? “A bit farther than that.”  
“You’re an alien!!”  
“No…(Yare yare) well, close enough.”  
“So why?” Nagisa asked. He seemed to have completely recovered from the shock of certain death, and now stood in his usual pose. Not cocky or reserved, but unfazed.  
“Why what?”  
“Why would you lie?”  
“Because then you’d ask me to kill KoroSensei,” This much talking and honesty was getting uncomfortable. He might end up teleporting away from his problems.  
“You can?”  
Korosensei had gotten over the attempted bombing of his students and his regular smile was now imprinted on his face. “Now now, class, I’m sure he wouldn’t be able to,” he coughed. “So you aren’t remaining to study with our class?”  
“No, I have 20 hours left in this universe”  
“So you’re staying with us until then.”  
“I was going to go and grab some coffee jelly from-”  
“Great! We can teach you some assassination moves!”  
They started to forcefully drag Saiki up the mountain, back into the classroom.  
“So Saiki,” Karma said, in a cheery tone, “Can you fix the moon?”  
“Yes, I’m powerful enough to.”  
“Will you fix it, please?”  
“No.”


End file.
